This invention relates to a small watercraft such as a personal watercraft and more particularly to an improved exhaust system therefore.
There is a very popular class of watercraft referred to as "personal watercraft." The watercraft that fall into this class are of a wide variety of types but have in common the feature that they are designed to be operated primarily by a single rider operator and which may carry no more than three additional passengers. Frequently, the operator sits in a straddle fashion and if passengers are accommodated they sit in tandem with the operator. This is not necessarily true in all cases but it does indicate the compact nature of this type of watercraft.
This type of watercraft is also quite sporting in nature. Because of these factors, conventional boaters have some objections to this type of watercraft.
One feature which is objected to by some people with this type of watercraft is the noise which they generate. The engine exhaust is generally silenced by utilizing a plurality of expansion chambers that are disposed between the exhaust ports and the point of discharge of the exhaust gases to the atmosphere. Because of the small space available, more sophisticated exhaust systems like utilize an automotive or larger power boat applications are not possible.
Also, it is the conventional practice with many types of water propulsion systems to silence the engine exhaust noises by cooling the exhaust gases either through water jacketing the exhaust system or by dumping cooling water from the engine cooling jacket into the exhaust system. Frequently, both of these expedients are combined.
These types of systems are effective for some sound frequencies, but not all of those experienced with engines, particularly of the two cycle type. Because of the fact that there may be a high quantity of water in the exhaust, this makes the use of other types of exhaust silencers difficult.
It is, therefore, a principal object of this invention to provide an improved silencing system for a personal watercraft.
Many of the silencing devices employed for silencing exhaust sounds at certain frequencies or certain running conditions provide restriction in the air flow and can reduce maximum power output.
It is, therefore, a further object of this invention to provide an improved exhaust silencing device that can be utilized to provide silencing under some running conditions and which silencing is accomplished by restricting the exhaust flow but which, under other running conditions, does not provide this effect.